1. Field of the Invention
This invention relates to a printer having one end of paper bail separated from a platen and the other end thereof contacting the platen and, more particularly, to a printer having a separating device for separating a paper bail, having one end of paper bail separated from a platen and the other end thereof contacting the platen, from the platen at the time of a paper feed operation.
2. Description of Related Art
Conventionally, printers have a printhead mounted on a carriage that moves along a guide shaft parallel to a cylindrical platen. The print paper is discharged upward through a space between the platen and the printhead from a lower side of the platen. Paper bail rollers are provided to bring the paper into close contact with the platen at the print position of the printhead. The paper bail rollers are rotatably attached to a paper bail shaft. Both ends of the paper bail shaft are fixed to the ends of arms that are capable of rotating to the same displacement around the same axis. Thus, the paper bail shaft is always moved substantially in parallel to the platen.
In printers of this type, paper bails are manually moved from a position in contact with the platen when the paper is initially being fed. The paper is wound around the platen from the back side to the upper front side through a space between the platen and the printhead. After the print paper has been wound around the platen, the paper bail shaft is returned to the original position in pressure contact with the platen with the paper therebetween.
There is also a type of printer in which the paper bails are moved by an actuator, for example, a motor. In this type of printer, cams are abutted against one or both of the arms so that the paper bails are moved between a position in contact with the platen and a position separated from the platen according to the displacement of the cams.
In both types of printer, however, the paper bail shaft remains substantially parallel to the platen during movement.
In the printers mentioned above, the printhead is positioned near the platen. Accordingly, in the printers having the characteristics described above, the paper bail shaft generally abuts the printhead and may be prevented from being sufficiently separated from the platen. If paper is fed while in this state, the paper is pressed against the platen by the printhead, on the side of the platen where the printhead is located, to pass through a space between the paper bail and the platen. However, on the other side, where the printhead is not located, and the paper is not pressed against the platen by the printhead, the paper tends to separate from the platen and the paper cannot pass through the space between the platen and the paper bail because the space is small. As a result, the paper bail shaft becomes an obstacle at that side in the manual paper feed mode, which slows the paper feed operation.
There is also a problem in the automatic paper feed mode. Again the paper is pressed against the platen by the printhead on the side where the printhead is located, and the paper passes through a space between the paper bail and the platen. On the other side of the platen, the paper does not pass through a space between the paper bail and the platen because the sheet cannot be adequately curved. This is particularly true if the hardness of print paper is high. Therefore, the tip end of paper cannot be inserted through a space between the platen and the paper bail roller on the side away from the printhead if the space between the platen and the paper bail roller is small.